The invention relates generally to a system for nondestructive inspection of parts, and more particularly, to a system for detecting flaws in parts employing eddy current techniques.
Coating systems are employed throughout many mechanical parts and systems, such as gas turbine engines. Such coating systems provide protection from elements such as, but not limited to, interference rubs, and high temperatures and so forth in harsh environments in which gas turbine engines operate. Components, such as seal teeth, employ coatings to improve wear and corrosion resistance and extend their useful lives. Moreover, such components undergo stress over a period of time and must be inspected under the coating, periodically to avoid damage to the engine.
There are several widely used nondestructive inspection techniques for detecting flaws in such coating systems. One commonly used technique is a fluorescent penetration inspection (FPI) technique. In the FPI technique, the coating is first removed from a coated part before inspecting a base metal of the part for cracks and flaws. A liquid fluorescent is penetrated into the part that is cleaned and is allowed to adsorb into features such as cracks and other flaws in the part. The part is further exposed to an ultraviolet radiation causing trapped penetrant to fluoresce. The part is recoated after inspection and cleaning.
The FPI technique typically has a limited detection capability with a low probability of detection, and its reliability is highly dependent upon process parameters and experience of an operator in interpreting an indication as a flaw. For example, a flaw indication may be misinterpreted or missed due to background noise. Furthermore, removal of coating before inspection is time consuming, often not economically feasible or quite expensive, and may cause potential damage to the part.
Accordingly, there is a need for an improved inspection technique for detecting flaws in a surface and sub-surface region of coated and uncoated systems.